Apparatus for trimming slate

ABSTRACT

A trimming apparatus for slate blanks wherein two opposing circular wheels are used to trim the blanks and at the same time accommodate warpage and irregularities in the blanks in order to furnish high production with relatively small breakage.

United States Patent 91 Field of Search ..225/98, 99, 3, 93; 125/23 Cabell et al. [451 Apr. 3, 1973 [54] APPARATUS FOR TRIMMING SLATE [56] Refer n es Cited [75] Inventors: Robert G. Cabell, Colombia; UNITED STATES PATENTS Thomas A. Yancey, Arvonia; Roy Norman i iu Daniel J. H i g 2,731,961 1/1956 Ponseele ..125/23 R FOREIGN PATENTS OR APPLICATIONS 1731 Assign: Arwmmuckingh, 76,830 5/1950 Norway ..12s/23 pany, Inc., Arvoma, Va.

22 Filed; 15 1967 Primary ExaminerHarold D. Whitehead AltorneyAuzville Jackson, Jr. [21] Appl. No.: 691,059

[57] ABSTRACT [52] US. Cl. .125/23 T A trimming apparatus for late blanks wherein two 0p- [51] Int. Cl. "328d 1/32 posing circular wheels are used to trim the blanks and [58] at'the same time accommodate warpage and irregularities in the blanks in order to furnish high production with relatively small breakage.

11 Claims, 6 Drawing Figures mrmrmle PATENTEUAPRB I975 3,724,439

SHEET 1 BF 3 INVENTORS l2 Roberf G. Gabe/l Thomas A. Yancey R 0y Norman L in w'l/e BY Dan/'e/ J. Harrington ATTORNEY PATENIEDAPM um 3,724,439

' SHEET 2 BF 3 46 NEE-44 INVENTORS Robert 6'. Cube/l Thomas A Yancey Roy Norman L/hV/Y/e Don/e/ J Honing/on PATENTEUAPRIs I975 3,724,439

SHEET 3 [1F 3 IN VENT 0R5 Robert 63 Gabe/l Thomas ,4. Yancey Ray A/ormanL/nv/l/e an/l J. Harrington ATTORNEY APPARATUS FOR TRIMMING SLATE BACKGROUND OF THE INVENTION 1 Field of the Invention The present invention relates to an automatic trimming apparatus for slate blanks and the like and in particular to an apparatus that will trim the blanks by conveying them past two opposed circular trimming wheels which are arranged to accommodate warpage and irregularities present in the blanks.

2. Description of the Prior Art The conventional apparatus for trimming slate as presently used in the slate industry dates back to the beginning of the 19th Century. It is a device wherein the slate is positioned by hand over a solid'unm'oving back-up stake against which the slate is trimmed by a scissor-like action of a curved blade oscillating in a vertical direction about a pivot located at one end of the stake. The oscillating blade is caused to oscillate about the pivot by a power means and the slate is fed to a cutting position when the blade is in the open period of a straight line duringthe first stroke in a manner to give the largest rectangular area in a given blank of raw material. Since the cutting blade and stake are spaced from one another, the slate is bevelled simultaneously with the trimming operation. This primative means of trimming slate involves considerable hand labor and the combination of the great amount of labor used and the high scrap rate add up to the operation of trimming and bevelling being very expensive and in long-time need for substantial improvement. Asimilarly deficient trimming device which is currently used, especially 'for thicker slates, has a helical blade similar to that of a reel type lawn mower.

In the patent literature a number of other trimming and bevelling arrangements have been suggested such can not easily twist about a vertical axis and conveys the slate along a conveying line past a trimming and bevelling station. The trimming and bevelling station consists of two opposed circular trimming wheels spaced in a manner that the slate is broken successively as it passes between the two wheels in a relatively straight line. The trimming wheels are arranged so that irregularities and warpage in the slate blank can be accommodated without causing excess difl'erential stresses in the slate which would result in irregular breaks not in a straight line or breaks on a line other than the trimming line and therefore make an unacceptable shingle. Also the circular nature of the trimming wheels create an ever narrowing nip as the slate passes into them so that a gradual shearing force is built up and causes a series of small little breaks that follow a substantially straight line although there are slight irregularities in the straight line. These slight irregularities lend to the character or personality of the shingle and are much wanted in the final product. Its the major breaks such as at the comers which deviate from the straight line so far that the slate is unusable that causes the high scrap rate of the old methods of trimming slate. Still further, the apparatus of the present invention has the conveyor means and at least one of the trimming wheels power drivenall at substantially the same rate so that the slate is conveyed into the trimming device at substantially the same rate as the peripheral rate of the trimming wheel. While one edge is being trimmed in the manner abovedescribed, the apparatus provides a second trimming and bevelling station opposite from the first one so that the opposite edge can be trimmed simultaneously. Means are provided so that the left bevelling and trimming station can be adjusted to accommodate different widths of slate. A similar duplicate apparatus insofar as the conveying and trimming and bevelling is concerned can be provided for the remaining two untrimmed edges which are at perpendicular to the first two edges. Still further, the conveying means of the apparatus is provided so as to accommodate and clamp slates having irregularities in surfaces and thicknesses with sufificient as the sawing of the edges or breaking of small chips in a straight line which is tantamount to a sawing. Another suggestion has been to use a single roll to break the slate over a solid stake. For one reason or another none of these techniques for trimming and bevelling are commercially used at the present timefll'heir deficiencies did not provide an economic, salable product for one reason or another. Either the breakage rate was too high or they produced an almost square edge when a properly bevelled edge was essential for most of the application of slate shingles or some other fault manifested itself.

SUMMARY OF THE INVENTION In accordance with the present invention, the hand labor involved in trimming and bevelling slate has been largely eliminated and the loss of slate through unnecessary breakage resulting from the previous trimming and bevelling methods has been greatly reduced. This has been accomplished through an apparatus which clampingly engages the slate so that it force as to be able to apply clamping and-traction pressures to keep the slate from either rotating substantially about a vertical axis or to prevent it from slipping while it is being nipped, trimmed and bevelled by the trimming wheels. Thus, the apparatus is able to automatically trim and bevel slate at a high rate of speed with minimum loss due to scrap and with a minimum amount of labor to control the operation.

Many objects and advantagesof the present inven tion will become apparent from the following description taken in conjunction with the accompanying drawings:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is. a simplified plan view of the apparatus of this invention;

FIG. 2 is a simplified elevation view of the apparatus of this invention;

FIG. 3 is a simplified elevation view of a part of FIG. 2 drawn to a larger scale in order to show greater details of the conveyor and trimming mechanism;

FIG. 4 is a perspective view of a trimmed and bevelled slate adapted for use on roofs, walls and the like made by the apparatus of this invention.

FIG. 5 is a large scale end view showing the interrelationship between a slate being trimmed and bevelled and the trimming wheels;

FIG. 6 is a view similar to FIG. 5 except that the slate is warped slightly above the surface of the lower conveyor;

DESCRIPTION OF THE PREFERRED EMBODIMENT As is illustrated in FIG. 1, the present invention is embodied in a slate trimming machine having a first station consisting of an entry table 10. The entry table has a series of rollers 1 1 on the top over which the slate blank 12 can be moved until the leading edge of the blank projects into the nip of the two pairs of opposed traction conveying means which will be described more fully later. The untrimmed slate is then grippingly engaged and caused to have its right side and left side passed into the nip defined by trimming means which shear the slate along two substantially straight lines with the slate outside the straight lines being broken away in small increments and permitted to fall downward from the machine. The slate with its now two trimmed edges is conveyed on past the right and left hand trimming stations onto a receiving table 15. It may then be passed through a similar machine to trim the remaining two edges of the slate. In the production of slate it is highly desirable to make the largest possible rectangle from the untrimmed blank. However, the schedule of standard roofing sizes for slate roofing provide for variation in width from six inches to 16 inches and in length from 10 inches to 26 inches with 45 possible combinations. In order to accommodate this variation, the apparatus as shown in FIG. 1 is provided with a double acting pneumatic cylinder 16 to push and pull the entire left pair of conveyor belts and trimming stations towards and away from the stationary pair of conveyor belts and trimming stations on the right side.

So that constant synchronized power can be applied to the adjustable left trimming means 14 and left pair of conveyor belts, the rotating drive shafts 18 have a fluted portion 17 so as to accept axial adjusting movement while continuing to supply rotary power. When two machines are used in series, the first machine is of a size to trim the length from 10 to 26 inches and the second machine is of a size to trim the width from 6 to l 6 inches.

In FIG. 2 a simplified elevation view of the apparatus just described in connection with FIG. 1 is shown. A suitable framework 19 supports a prime power source 20 which through a belt drive 21 from the power pulley 22 drives a shaft pulley 23 which drives the upper drive shaft. This upper drive shaft has a spur gear 24 fixed to rotate with the shaft which meshes with a spur gear 25 fixed to cause the lower drive shaft to rotate therewith at the same synchronized speed. The upper drive shaft also has a right trimming wheel drive pulley 26 (FIG. 1) which drives a wheel trimming drive pulley 27 mounted on the trimming wheel shaft 28 which rotates inside of bearings (not shown) in two mounting members 29. A similar arrangement is provided on the left side. Also, both the upper drive shaft and lower drive shaft have suitable drive pulleys or sprocket wheels 30 for the conveyor belts. As shown in FIGS. 2 and 3 the conveyor means comprises the upper conveyor belt in the form of a V-belt and the lower conveyor belt is in the form of a chain. The front end of the conveyor V-belts and conveyor chains rotate around suitable idle pulleys or sprockets 33 which are mounted on the front conveyor shafts 34. These idle pulleys and sprockets are not driven and are free to rotate at will along with the movement of the conveyor belts.

A side view of the entry table 10 along with the parallel rollers 11 is likewise shown in FIG. 2. In FIG. 3 a larger scale view in simplified elevation is shown in the details of the conveyor and trimming means of FIG. 2. It is to be noted that in the right trimming means 13 the axis of rotation 37 of the upper cylindrical trimming wheel 35 is slightly downstream from the normal axis 38 of the idling lower trimming wheel 36 which rotates about a lever arm 39 which itself rotates about an axis 40 almost directly below the axis of rotation of the lower trimming wheel but slightly upstream therefrom. The lever arm is biased by a tension spring 41 to move the lever arm in a counter-clockwise direction so that it will cause the lower trimming wheel to be both elevated and move slightly upstream.

The upper portion of the conveyor chain 32 bottoms and slides along a solid back-up steel plate 42. The lower surface of the V-belt 31 is mounted so as to be in opposition to the upper surface of conveyor chain 32 and is biased towards the upper surface of the drive chain by clamping means 43 which consists of a series of bogies 44 idling along the inner periphery and rotatingly driven by the movement of the V-belt. The bogies are pivoted in approximately the middle of a lever arm 45 which itself pivots at a downstream and lower end pivot 46 with the opposite end of the lever arm being biased by, a compression spring 47 in a downward direction. The amount of bias or compression of the spring is adjustable through a screw arrangement 48. Thus, in eflect, the bogies are mounted on a second-class lever biased in a downward direction to a blank clamping position by a compression spring.

Slate varies in thickness normally from approximately three-sixteenths to three-eighths inch; so, therefore, the upper belt must be free to bias between zero inches of clearance above the lower belt to about 1 inch clearance above the lower belt to accommodate not only variations in thickness of the slate being fed but warpage, convolutions and other irregularities in the slate itself. Thus, in FIG. 3, when the slate blank enters the approximately 1 inch spread or nip portion 49 of the conveyor means, it will gradually be engaged by the decreasing separation of the upper belt from the lower belt with increasing pressure being applied therebetween through the clamping pressure exerted by bogies 44 which are pressed downward by the compression springs 47. This clamping force is sufficient to prevent the slate blank from rotating about a vertical axis during the trimming operation. Furthermore, it applies sufficient traction force to positively feed the slate into the nip of the trimming wheels.

As is shown in FIG. 3 there is a slight separation between the lower chain and upper belt as represented by a piece of slate passing therebetween.

The upper cylindrical trimming wheel 35 is power driven at substantially the same peripheral rate of speed in the same direction as the conveyor belts 31 32 which move the slate blank into the trimming means. The lower cylindrical trimming wheel 36 in the embodiment shown is free to idle along at the same peripheral rate of speed as the conveyor means and the slate blank since it is biased to ride on the under side of the slate blank as it moves into the trimming station. Since the upper wheel is of fairly large diameter, the slate gradually moves into the nip between the two trimming wheels which applies an ever increasing pressure in the form of a tangential shear until the pressure is greater than the shear strength of the slate at which time the outer portion will break away and fall downwardly.

FIG. 4 is a perspective view of a trimmed and bevelled slate 12 adapted for use on roofs, walls and the like with the bevel converging towards the upper face. As is seen in FIG. 4, natural slate when cleaved along its normal cleavage planes has very pleasing irregularities referred to as character" in the industry. Also the slight irregularities along the trimmed and bevelled edges renders a pleasing appearance to the finished product. The total result is considered by the consuming public and the people in the trade and architects as providing a unique and highly attractive building material that is much sought after. However, the very things that lend the natural beauty to the slate have created the problems that have so long resisted the utilization of automatic machine methods for trimming and bevelling. Since such automatic machines would have to accommodate the natural irregularities of the material at a high rate of speed with a minimum amount of breakage. The principles employed in the present apparatus have accomplished such results and have constituted a great, much needed and long sought after advance in the art of automatically trimming and bevelling slate at high speed with minimum breakage.

FIG. 5 is a detailed view of a slate blank being trimmed and shows that normally the blank has its bottom portion resting on the chain 32 which in turns rests on the back-up plate 42. It is to be noted that the lower cylindrical trimming wheel 36 freely rotates on the underside of the slate in alignment with the upper surface of the chain. The upper power driven cylindrical trimming wheel 35 cooperates with the lower trimming wheel 36 to gradually nip the slate blank as it is fed between the two trimming wheels whereby the slate is caused to rupture, probably under tangential shearing forces, to an angle or bevel which runs approximately from the point of maximum pressure exerted by the upper trimming wheel to the point of maximum pressure exerted by the lower trimming wheel.

It is to be noted that the upper trimming wheel 35 lies almost entirely on one side of the slate blank except for the periphery of the wheel extending past the face of the blank sufficient to exert enough pressure to cause the edge of the blank to be trimmed and broken off outside of the trim line. In FIG. 5 this is an amount approximately equal to the thickness of the slate being trimmed.

It is also to be noted that the blank trim line 50 is in reality a bevelled edge bordered by an outer trim line 51 along the upper surface and inner trim line 52 along the lower surface. After the upper trimming wheel 35 has broken the slate away from outer trim line 51, it extends on past that surface of the slate. In normal operation, the lower trimming wheel 36 always lies fully on the opposite side of the slate and supports the slate blank inward from trim line 50 and causes the blank to be trimmed along the inner trim line 52. The slate blank thus has its edge caught between the two opposing forces of the upper trimming wheel 35 along its peripheral trimming edge 53 and the lower trimming wheel 36 along its peripheral supporting and trimming surface 54. The maximum pressure is exerted between the two closest points on these opposed trimming wheels during that part of the nip when they are on opposite sides of the slate. As this pressure is increased, it exceeds the shear strength of the slate and it ruptures along a iine connecting these two pressure points. As shown in FIG. 5, this defines an approximately 45" bevel which can be changed depending on the spacing between the facing planes of the two trimming wheels.

FIG. 6 is a view similar to FIG. 5 but here is shown the slate blank elevated above the upper surface of the conveyor chain 32. This represents a warped position as probably the forward and rearward edges of the slate blank are resting on the conveyor chain and the portion being cut as shown in FIG. 6 is bowed away from the conveyor chain and therefore unsupported on its underside except for the lower trimming wheel 36 which is biased upward by lever 39 and spring 41. Thus, although the blank has bowed away from the straight conveying line represented by the top surface of the conveyor chain, it is still supported by the lower trimming wheel with sufficient counterforce to the upper trimming wheel to cause the trim line to remain substantially straight. The importance of the accommodation of this warpage and other similar irregularities in the blank cannot be overemphasized because without such accommodating means to cause the opposed trimming wheels to always be in contact with the blank to exert a positive shearing force between said trimming wheels regardless of the warpage or other irregularities, the scrap rate would be so high as to reduce much of the meritorious advance represented by the invertor. Obviously other means can be provided which would be equivalent to the illustrated means for accomplishing this purpose.

Although the apparatus of this invention has been described in FIGS. 3, 5 and 6 with reference to the right side conveying means and trimming means, it is to be understood that the left side conveying means and trimming means function similarly except for this adjustability towards and away from the right side.

A slate blank is first placed on the entry table 10 with its right edge lined up with the right trimming means 13 in a manner that a relatively straight trim edge can be made with a minimum of material to be broken away. The maximum length that can be obtained from the slate blank is then determined and a control (not shown) actuated to move the double acting pneumatic cylinder 16 to position the left pair of conveyor belts and left trimming means 14 in a position to cause a trim edge to be made of the maximum useable length obtainable from the slate blank. The slate blank is then pushed into the nip of the conveyor which is constantly running during normal operation whereby the blank is picked up, clamped and moved past the right and left trimming means which simultaneously trim and bevel relatively straight lines on both the right and left side of the blank. The blank continues to be conveyed through the apparatus until it is deposited on a table 15 at the exit side of the apparatus. The blank can then be passed through the same apparatus or a similar apparatus for trimming the remaining two sides after which it is further processed by punching nail holes and the like. Obviously, only one trimming cut needs to be made at a time although two trimming cuts are made simultaneously in the disclosed apparatus.

In as much as the preferred embodiment of the present invention is subject to many modifications, variations and changes in details, it is intended that all matter contained in the foregoing description or shown on the accompanying drawings shall be interperted as illustrative and not in a limiting sense.

What is claimed is:

1. Apparatus for trimming slate blanks and the like comprising a trimming means for trimming an edge of said blank along a substantially straight beveled edge comprising two trimming elements, a conveyor means for causing relative movement between said blank and said trimming means so that said edge of said blank passes through said trimming means along a substantially straight line, said trimming means including as a first trimming element a rotating circular trimming wheel and as a second trimming element an opposed supporting and trimming means, said trimming wheel lying mostly on one side of said blank and having a peripheral trimming edge adjacent the outside edge of said beveled edge which is adapted to exert sufficient pressure on the blank to cause the material outside of said beveled edge to be broken away, said opposed supporting and trimming means lying on the opposite side of said blank from said trimming wheel and having a supporting and trimming surface spaced inward from said wheel and adapted to-support the blank inward from said outside edge and define the inside line of said bevel so that a blank edge passed between the trimming wheel and the supporting and trimming surface will be progressively broken ofi along a substantially straight beveled edge, and vertically movable means mounting at least one of said trimming elements for vertical movement in response to irregularities or warpage in the slate for accommodating warpage and other irregularities of the blank being trimmed, and means for driving said conveyor means.

2. The invention as recited in claim 1 wherein said opposed supporting and trimming means is in the form of a rotating circular wheel having a peripheral supporting and trimming surface.

3. The invention as recited in claim 2 wherein both of said wheels rotate at a peripheral speed substantially equal to the rate at which said blank moves through said trimming means.

4. The invention as recited in claim 3 wherein at least one of said wheels is power driven at a peripheral speed substantially equal to the rate at which said blank moves through said trimming means.

5. The invention as recited in claim 4wherein said conveyor means includes two opposed endless conveyor belts.

6. The invention as recited in claim 5 wherein said conveyor belts are caused to clamp a blank therebetween by a plurality of spring biased bogies.

7. The invention of claim 5 wherein the planes of said wheels are spaced from one another a sufiicient distance to cause the blank to be' bevelled simultaneously with the trimming.

8. The invention of claim 5 wherein the conveyor means and the trimming means are all driven by a power source at synchronized speeds so that said blank is conveyed into the trimming means at the same speed the trimming means is being driven.

9. The invention of claim 5 wherein the conveyor means and the trimming means are all driven by a single prime power source at synchronized speeds so that said blank is conveyed into the trimming means at the same speed the trimming means is being driven. I

10. Apparatus for trimming slate blanks and the like comprising a trimming means for trimming an edge of said blank along a substantially straight beveled edge, a conveyor means for causing relative movement between said blank and said trimming means so that said edge of said blank passes through said trimming means along a substantially straight line, said trimming means including a first rotating circular trimming wheel and an opposed second rotating circular trimming wheel, said first trimming wheel lying mostly on one side of said blank and having a peripheral trimming edge adjacent the outside edge of said beveled edge which is adapted to exert sufficient pressure on the blank to cause the material outside of said beveled edge to be broken away, said opposed second trimming wheel lying on the opposite side of said blank from said first trimming wheel and having a supporting and trimming surface spaced inward from said first trimming wheel adapted to support the blank inward from said outside edge and define the inside line of said bevel so that a blank edge passed between the first trimming wheel and the supporting and trimming surface of the second trimming wheel will be progressively broken off along a substantially straight beveled edge, and vertically movable means mounting at least one of said trimming wheels for vertical movement in response to irregularities or warpage in the slate for accommodating warpage and other irregularities of the blank being trimmed, and means for driving said conveyor means.

11. Apparatus for trimming slate blanks comprising a trimming means for trimming an edge of said blanks along a substantially straight trim line comprising two trimming elements, a conveyor means for causing relative movement between said blank and said trimming means so that said edge of said blank passes through said trimming means along a substantially straight line, said trimming means including as a first trimming element a rotating circular trimming wheel and as a second trimming element an opposed supporting and trimming element, said trimming wheel lying mostly on one side of said blank and having aperipheral trimming edge adjacent the outside edge of said trim line which is adapted to exert sufficient pressure on the blank to cause the material outside of said trim line to be broken away, said opposed supporting and trimming element 

1. Apparatus for trimming slate blanks and the like comprising a trimming means for trimming an edge of said blank along a substantially straight beveled edge comprising two trimming elements, a conveyor means for causing relative movement between said blank and said trimming means so that said edge of said blank passes through said trimming means along a substantially straight line, said trimming means including as a first trimming element a rotating circular trimming wheel and as a second trimming element an opposed supporting and trimming means, said trimming wheel lying mostly on one side of said blank and having a peripheral trimming edge adjacent the outside edge of said beveled edge which is adapted to exert sufficient pressure on the blank to cause the material outside of said beveled edge to be broken away, said opposed supporting and trimming means lying on the opposite side of said blank from said trimming wheel and having a supporting and trimming surface spaced inward from said wheel and adapted to support the blank inward from said outside edge and define the inside line of said bevel so that a blank edge passed between the trimming wheel and the supporting and trimming surface will be progressively broken off along a substantially straight beveled edge, and vertically movable means mounting at least one of said trimming elements for vertical movement in response to irregularities or warpage in the slate for accommodating warpage and other irregularities of the blank being trimmed, and means for driving said conveyor means.
 2. The invention as recited in claim 1 wherein said opposed supporting and trimming means is in the form of a rotating circular wheel having a peripheral supporting and trimming surface.
 3. The invention as recited in claim 2 wherein both of said wheels rotate at a peripheral speed substantially equal to the rate at which said blank moves through said trimming means.
 4. The invention as recited in claim 3 wherein at least one of said wheels is power driven at a peripheral speed substantially equal to the rate at which said blank moves through said trimming means.
 5. The inventioN as recited in claim 4 wherein said conveyor means includes two opposed endless conveyor belts.
 6. The invention as recited in claim 5 wherein said conveyor belts are caused to clamp a blank therebetween by a plurality of spring biased bogies.
 7. The invention of claim 5 wherein the planes of said wheels are spaced from one another a sufficient distance to cause the blank to be bevelled simultaneously with the trimming.
 8. The invention of claim 5 wherein the conveyor means and the trimming means are all driven by a power source at synchronized speeds so that said blank is conveyed into the trimming means at the same speed the trimming means is being driven.
 9. The invention of claim 5 wherein the conveyor means and the trimming means are all driven by a single prime power source at synchronized speeds so that said blank is conveyed into the trimming means at the same speed the trimming means is being driven.
 10. Apparatus for trimming slate blanks and the like comprising a trimming means for trimming an edge of said blank along a substantially straight beveled edge, a conveyor means for causing relative movement between said blank and said trimming means so that said edge of said blank passes through said trimming means along a substantially straight line, said trimming means including a first rotating circular trimming wheel and an opposed second rotating circular trimming wheel, said first trimming wheel lying mostly on one side of said blank and having a peripheral trimming edge adjacent the outside edge of said beveled edge which is adapted to exert sufficient pressure on the blank to cause the material outside of said beveled edge to be broken away, said opposed second trimming wheel lying on the opposite side of said blank from said first trimming wheel and having a supporting and trimming surface spaced inward from said first trimming wheel adapted to support the blank inward from said outside edge and define the inside line of said bevel so that a blank edge passed between the first trimming wheel and the supporting and trimming surface of the second trimming wheel will be progressively broken off along a substantially straight beveled edge, and vertically movable means mounting at least one of said trimming wheels for vertical movement in response to irregularities or warpage in the slate for accommodating warpage and other irregularities of the blank being trimmed, and means for driving said conveyor means.
 11. Apparatus for trimming slate blanks comprising a trimming means for trimming an edge of said blanks along a substantially straight trim line comprising two trimming elements, a conveyor means for causing relative movement between said blank and said trimming means so that said edge of said blank passes through said trimming means along a substantially straight line, said trimming means including as a first trimming element a rotating circular trimming wheel and as a second trimming element an opposed supporting and trimming element, said trimming wheel lying mostly on one side of said blank and having a peripheral trimming edge adjacent the outside edge of said trim line which is adapted to exert sufficient pressure on the blank to cause the material outside of said trim line to be broken away, said opposed supporting and trimming element lying on the opposite side of said blank from said trimming wheel and having a supporting and trimming surface spaced inward from said wheel and adapted to support the blank inward from said trim line, vertically movable means mounting at least one of said trimming elements for vertical movement in response to irregularities or warpage in the slate for accommodating warpage and other irregularities of the blank being trimmed, and means for driving said conveyor means. 